Welcome! Believe it or not this dilemma is more common then you think! The more you work with Leather the more you will want to try new projects and eventually you will want some nice stitiching to finish off a proiject.
Hand stitching is by far the best way to assemble projects, however it is an art. Those that can do it well deserve praise because it takes time, effort and skill to make good looking stitches. Machine stitching is the next best choice but many machines are costly and do involve a bit of a learning curve. If you are doing small projects like a Knife sheath or small case you can get by with hand stitching, but if you plan to do belts or bigger projects a machine can be a blessing. Here is what i found to be the basics;
Hand Stitching- A good awl, needles, good thread, bees wax, Al Stolhmans book on Hand Stitching, Stitching horse cost to start about $60-
Tipmann Boss- An entry level machine that you can learn on is easy to operate and when you are ready to move up to a better machine you can sell for very close to what you paid for it! Cost $1400-
Artisan Leather StitcherToro 3000- The "Cat's Pajamas" for crafters. The machine that everyone loves! Will do everything you need and more Cost- $2200-
Whatever you choose good luck and remember to have fun!